1. Field of the Invention
The present invention generally relates to networks using cross-connect units at telecommunication nodes, and more particularly to an automatic restoration method in a mesh network.
A synchronous transfer mode (STM) network and an asynchronous transfer mode (ATM) network capable of transmitting audio and visual data at a high speed have been in use in recent years to provide various services. One example of such a network is a mesh network in which telecommunication nodes provided with cross-connect units and telecommunication links are arranged in a mesh configuration.
Such a network should be configured so as to be capable of continuing to serve the user in the event of a failure. Continuation of services requires that a failure occurring in the network be automatically detected and telecommunication paths that enable bypassing of the failure be established. An automatic restoration method is an essential algorithm specifying a procedure for establishing the paths.
2. Description of the Prior Art
There are generally two types of automatic restoration methods proposed for mesh networks: the pre-planned restoration method and the dynamic restoration method. In the pre-planned restoration method, a configuration map specifying alternate paths is stored at each cross-connect unit.
In the event of a failure, alternate paths are set according to the configuration map. Hence, a high-speed restoration is possible. Information relating to the alternate paths is computed by the central Operation Systems and distributed throughout the nodes.
In the dynamic restoration method, each node is not provided with the above-described configuration map. In the event of a failure, nodes adjacent to the point of failure exchange restoration-related messages several times so as to find alternate paths.
However, the above-described conventional technology has the following problems. In the pre-planned restoration method, the process executed by the central Operation Systems to distribute the information relating to alternate paths to the nodes may be complex and lengthy. Further, when an additional failure (i.e., a secondary failure) occurs during the computation for finding alternate paths or during the distribution of the information, an updating computation and a distribution of the updated information to the nodes are required. Hence, the process required for the restoration becomes complex. Further, since each node is required to store the information in a memory, restoration capabilities for various failure scenarios are limited.
In the dynamic restoration method, restoration messages are exchanged between the nodes to search for alternate paths. Hence, a prompt restoration cannot be hoped for in comparison with the pre-planned restoration method.
Accordingly, an object of the present invention is to provide a telecommunication node, a restoration method and a telecommunication network, wherein the aforementioned problems are eliminated.
Another and more specific object of the present invention is to provide a telecommunication node, a restoration method and a telecommunication network, wherein a prompt restoration is possible using a simple process.
The aforementioned objects can be achieved by a restoration method in a telecommunication network in which each node is provided with physical topology information relating to a physical construction of telecommunication paths included in the telecommunication network and logical topology information relating to routing of telecommunication paths, said restoration method comprising the steps of:
(a) transmitting information relating to a failure that has occurred in the telecommunication network, throughout the network;
(b) in each node that has received said information relating to the failure, determining alternate paths for bypassing the failure using said information relating to the failure, said physical topology information, and said logical topology information; and
(c) switching services to the alternate paths determined in step (b).
The aforementioned objects can also be achieved by a telecommunication node provided with physical topology information relating to a physical construction of telecommunication paths included in the telecommunication network and logical topology information relating to routing of telecommunication paths, said telecommunication node comprising:
first means transmitting information relating to a failure that has occurred in the telecommunication network, throughout the telecommunication network;
second means determining alternate paths for bypassing the failure using said information relating to the failure, said physical topology information, and said logical topology information; and
third means switching services to the alternate paths determined by said second means.
The aforementioned objects can also be achieved by a telecommunication network including telecommunication nodes each provided with physical topology information relating to a physical construction of telecommunication paths included in the telecommunication network and logical topology information relating to routing of telecommunication paths, wherein each node comprises:
first means transmitting information relating to a failure that has occurred in the telecommunication network, throughout the telecommunication network;
second means determining alternate paths for bypassing the failure using said information relating to the failure, said physical topology information, and said logical topology information; and
third means switching services to the alternate paths determined by said second means.
According to the restoration method, the telecommunication node and the telecommunication network of the present invention, restoration from failure is attained by using topology tables relating to the entirety of the network. Only information (message) relating to a failure needs to be exchanged for restoration. Therefore, the present invention realizes a high-speed restoration from failure with smaller volume of messages exchanged as compared with the conventional dynamic restoration method.
In further accordance with the present invention, reception of information relating to a failure is properly controlled so that cross-connection in a node is prevented from being executed in a transient state in which latest information relating to a failure has not arrived yet. Accordingly, it is possible to restore from failure using the latest topology information.
According to one preferred embodiment of the present invention, topology information is automatically updated so that the nodes in a network are provided with latest topology information relating to the entirety of the network which information is necessary for cross-connecting process executed in the event of a failure.
By executing, in each node, computation for finding alternate paths adapted for typical scenarios such as those involving a single link failure or a single node failure, a high-speed restoration from failure is realized.
According to another aspect of the present invention, restoration from failure can take place only by switching from a failed path to an alternate virtual path. Thus, a high-speed restoration is realized.
In further accordance with the present invention, alternate path selection most suitable for a failure type is employed so that a high-speed restoration is realized.